1 Routing variables

These are the basic variables defined by the routing layer of PSYC. How these variables interact in unicast and multicast packet routing can be read on Spec:Routing.

• _source - The source entity uniform the packet comes from.
• _target - The recipient entity.
• _context - The context (a chatroom, a newsroom, a presence subscription or other group or channel).
• _length - The length of the content part of a Packet.
• _source_relay - The original sender of a message. Eg. set to the participants uniform when a group relays messages to it's participants.
• _tag - A tag that should be refered to when this message is replied to or forwarded. The tags can be used to associate replies to their original requests. (Implementations might use callbacks to signal a response to a request).
• _tag_relay - The original tag of the message this message is a reply to or forward of.

During the process of routing keyword inheritance is not in effect. A _source_relay MUST NOT be treated as if a _source was given. Inheritance is to be applied to routing variables only in the entity layer.

1.1 Tagging

The routing variables _tag and _tag_relay are used to implement a special behaviour called Tagging in PSYC.

It is mostly used to map a response back to its request and gives the sender a way to easily figure out which replies were triggered by packets it sent and thus handle responses asynchronously.

When an entity receives a packet it MUST copy the contents of the _tag variable to the _tag_relay variable of the response.

The contents of _tag is opaque and can be an arbitrary value. It is strongly recommended to generate globally unique ids for tags.